The present invention relates to a speaker voice coil and a speaker unit using the same.
As shown in FIG. 1, a speaker voice coil 10 conventionally has a wire winding part 12 which is made of a single or plurality of layers of wire 12A wound around a voice coil bobbin 11. The voice coil bobbin 11 has a film-like or cylindrical shape, being made of kraft paper, a metal film such as titanium and aluminum, or a heat resistant sheet such as a polyimide film. The wire 12A is a conductor such as copper, aluminum, and copper-clad aluminum, covered with a resin coating (insulating coating or adhesive coating).
The conventional speaker voice coil described above has had the following problem. That is, the voice coil 10 structurally has a low efficiency in converting an input electric signal into an acoustic signal. When high power is input to the voice coil 10, an electric current flowing through the wire 12A therefore generates a large amount of Joule heat. This gives rise to the problem that the resin coating that covers the wire 12A is gradually melted or decomposed by heat, and the binding between the voice coil bobbin 11 and the wire winding part 12 and the binding between the turns of the wire 12A become loose.
Losing tight binding with the voice coil bobbin 11 or between the turns of the wire 12A, the wire winding part 12 can shift from its predetermined mounting position due to amplitude operations of the speaker, and cause such failures as disconnection and coming off the voice coil bobbin 11.
In order to solve this problem, there have been proposed such methods as shown in FIGS. 2A to 2C. In the method of FIG. 2A, the voice coil bobbin 11 and both upper and lower ends (coil ends) of the wire winding part 12 are fixed with an adhesive 13. In the method of FIG. 2B, the lower end of the voice coil bobbin 11 is bent outward in advance. In the method of FIG. 2C, the lower end of the voice coil bobbin 11 is bent outward to form a U-sectioned accommodating part 14, in which after the wire winding part 12 is accommodated, the accommodating part 14 is filled with an adhesive 13 for sealing (for example, see Japanese Patent Application Laid-Open No. Hei 08-168095).
According to the first method, however, the adhesive 13 can suffer damage such as heat melting, heat decomposition, and deterioration from Joule heat that is generated by the current flowing through the wire 12A to the adhesive 13. The reinforcing effect then disappears under high-temperature environment.
According to the second method, if the voice coil bobbin 11 is made of conductive material, eddy currents can occur with a problem of increased mechanical resistance.
According to the third method, there is the problem that the usage of the adhesive 13 is high since the entire wire winding part 12 is fixed by the adhesive 13.
Another problem is that it is difficult to bend the end of the voice coil bobbin 11 outward so as to accommodate the entire wire winding part 12. In particular, when the voice coil bobbin 11 is made of a hard metal such as titanium, bending the voice coil bobbin 11 can damage the wire winding part 12 with a problem of short circuit.